(1) Field of the Invention
The present invention relates to a wholly aromatic polyamide copolymer. More particularly, the present invention relates to a wholly aromatic polyamide copolymer containing, as a portion of the aromatic diamine moiety, a methyl- or chloro-benzidine structure and having an excellent heat, flame and chemical resistance, solubility in organic solvents and shaping property, and useful for shaped articles having a superior mechanical strength and modulus of elasticity.
(2) Description of the Related Arts
It is known that wholly aromatic polyamide (aramid) resins have a superior mechanical strength and modulus of elasticity and an excellent heat resistance, and thus are useful for fibers, films and other shaped articles. Especially, a para type aramide resin, namely poly-p-phenylene terephthalamide (PPTA) resin, is a typical aramide resin useful for industrial materials and protecting devices in which the specific properties of the aramide resins are effectively utilized. Nevertheless, the PPTA resin poses problems in the polymerization thereof and has an unsatisfactory spinnability and formability due to a high rigidity or stiffness of the PPTA molecules. For example, in the production process of the PPTA resin, hexamethylphosphortriamide, which has a high toxity for the human body and other life-forms, must be used as a polymerization medium. Also, in the production of PPTA fibers, films or other shaped articles, a concentrated sulfuric acid must be employed to prepare a liquid crystalline dope solution of the PPTA resin and a liquid crystal spinning or shaping procedure must be carried out. After this procedure, the sulfuric acid in the resultant product must be neutralized with a large amount of a neutralizing agent. Also, the resultant product (fibers or other shaped articles) contains inorganic ions derived from the sulfuric acid and the the neutralizing agent, and these inorganic ions cause a lowering of the quality of the product. Further, removal of the inorganic ions raises the cost of the resultant product.
To eliminate the above-mentioned disadvantages, attempts have been made to employ a popular organic polar solvent for the dope solution of the PPTA resin, to prepare an isotropic dope solution and to simplify the spinning or shaping procedure. Particularly, Japanese Unexamined Patent Publication Nos. 51-76,386, 51-134,743, 51-136,916, 61-252,229, 62-27,431, 62-225,530, 62-177,022 and 62-177,023 disclose methods for enhancing the solubility of the aramide resins, to introduce ether bonds into the aramide molecules by copolymerization.
In one such attempt, wholly aromatic polyamide copolymers prepared by the copolymerization of an aromatic diamine component comprising p-phenylene diamine (PPDA) and 3,4'-diaminodiphenylether (3,4'-DAPE) with an aromatic dicarboxylic component comprising terephthalic acid, have a high mechanical strength, modulus of rigidity and chemical resistance, and can be prepared by using a popular polar solvent, for example, N-methylpyrrolidone, as the polymerization medium. Also, the resultant polymer solution can be directly utilized as a dope solution for spinning or other shaping processes. Therefore, the above-mentioned ether-bond-containing wholly aromatic polyamide copolymers provide a greatly improved process for producing shaped aramide resin-articles.
Nevertheless, the introduction of the ether bonds usually causes the resultant wholly aromatic polyamide copolymer resins to exhibit an unsatisfactory heat resistance and modulus of rigidity, which can be assumed from the primary structure of the resultant aramide copolymer molecules.
Accordingly, there is still a strong demand for a new type of wholly aromatic polyamide resins having a satisfactory mechanical strength, heat resistance and modulus of rigidity, and capable of being produced by an easy polymerization process and of being shaped by an easy shaping process.